The present invention relates to a programmable remote control transmitter and, more particularly, to an transmitter driver for a programmable remote control transmitter to emulate any one of transmitters for remote-controlling electrical devices.
Various types of electronic products have been used at home to provide convenience in daily life in recent years. Most electric products have so-called remote controllers as transmitters for electrically remote-controlling the electric devices. Since every electric device a transmission system of a unique type, a another electric device. If the number of electric devices is increased, the number of types of transmitters is accordingly increased. When a large number of remote controllable electric devices are installed in a house, the user is often confused of selecting a transmitter appropriate for each electric device.
In order to solve this problem, the present applicant has proposed a programmable remote control transmitter. This programmable remote control transmitter receives various remote control codes from all transmitters used in the house and decodes these codes. The decoded remote control codes are stored in a memory. Where the remote control transmitter is used, a type of the electric device to be available is selected and the selected electric device is irradiated with ultrasonic waves or infrared rays, thereby controlling the electric device in accordance with data stored in the memory which corresponds to the remote control codes of the selected electric device. Such a conventional programmable remote control transmitter is described in detail in Japanese patent prepublication No. 60-254898 which corresponds to U.S. Pat. No. 4,623,887 issued to K. B. Welles, II on Nov. 18, 1986.
However, with this arrangement, electric devices to be controlled have different output signal formats. For this reason, since the operating characteristics of a transmitter differ in accordance with the output signal formats, it is difficult to drive the transmitter under the optimal operating conditions. In other words, a transmitter driver used in the remote control transmitter normally comprises an output transistor for receiving an electrical signal representing a remote control code and a transmitter, such as a light-emitting diode, connected to its output side. Therefore, the conventional transmitter used in such a driver has been designed with reference to a case wherein a maximum current is supplied thereto, e.g., a remote control code signal of a continuous wave format is used. In this case, when the different output wave formats are used, a current supplied to the transmitter increases or decreases, thus varying an effective output of the transmitter. As a result, a controllable range of the remote control transmitter differs in accordance with the selected electric devices, thus confusing a user. Typical output wave formats will be exemplified below. For example, in a continuous wave format, a ratio of a pulse burst period to a pulse off period, i.e., a duty ratio, is 50%. In a gated carrier format, the duty ratio is 3 to 10%, and in a single pulse format, the duty ratio is 0.5 to 1%. Therefore, when a circuit is designed such that a current of 100 mA is supplied to a transmitter in the continuous wave format, only a current of 20 mA and a current of 2 mA are supplied thereto in the gated carrier and single pulse formats, respectively. As a result, the transmission distances of the transmitter output in the gated carrier and single pulse formats are shorter than that in the continuous wave format.